The nitration of hydrocarbons produces a variety of products, depending on the reaction conditions and the feedstock compositions. For example, vapor phase nitration of propane typically results in a mixture of four nitro-paraffin products: nitromethane, 1-nitropropane, 2-nitropropane, and nitroethane in essentially fixed relative concentrations. High pressure nitration of propane can selectively produce 2-nitropropane over other lower molecular weight nitroalkanes like 1-nitropropane, nitromethane, and nitroethane. The high pressure nitration of cyclohexane typically results in the formation of cyclohexanol, cyclohexanone, nitrocyclohexane, and oxidation products.
The byproducts from typical vapor phase and high pressure nitration of propane, can have similar boiling points, especially among the low molecular weight nitroalkanes (2-nitropropane, 1-nitropropane, nitromethane, and nitroethane), making separation difficult. A conventional post-reaction distillation sequence uses tall columns and high reflux ratios, which are expensive and consume a lot of energy. Other conventional separation methods use an additional mass-separating agent to recover the desired nitro-paraffin. A need exists, therefore, for more economical and energy efficient processes for recovering desired nitroalkane products.